[thinkyhead]

Description

DGUSDisplay::writeVariable(uint16_t, int16_t) swaps bytes with (value & 0xFFU) << 8U | (value >> 8U) on the signed value. For a negative value, value >> 8 sign-extends, and the OR overwrites the high byte with 0xFF. So most negative numbers reach the display wrong:

Value	Sent before	Display shows	Sent after
-2	FF FF	-1	FF FE
-125	FF FF	-1	FF 83
-300	FE FF	-257	FE D4

This change sends the value through the existing uint16_t overload, so the swap is done on an unsigned value.

The path is used by sendFloatAsIntValueToDisplay, e.g. for a negative probe Z offset shown with 2 decimals (-1.25 is sent as -125 and shows as -0.01).

The CR6Community fork had already fixed this in its own copy of the DGUS code. I found it while porting that fork's work for #19958.

Requirements

A classic DGUS display: DGUS_LCD_UI ORIGIN, FYSETC, HIPRECY or MKS. DGUS Reloaded and the other DWIN UIs have their own code and aren't affected.

Benefits

Negative values (e.g. Z offset) display correctly on classic DGUS screens.

Testing

• A host test of the old and new swap over all 65536 int16_t values: 32640 values were wrong before, none after.
• Built mega2560ext tests 1 (FYSETC) and 2 (MKS).
• Not tested on a display. Testers with an ORIGIN, FYSETC, HIPRECY or MKS screen and a negative Z offset are welcome.

Configurations

buildroot/tests/mega2560ext config-01 / config-02.

Related Issues

None filed. Found while working on #19958.